Magnetic storage cell

ABSTRACT

A horizontally disposed elliptical or rectangular magnetic memory cell includes at least two conductive lines to carry current and a magnetic element disposed between the conductive lines. The current through the conductive lines induces a magnetic field, such that the magnetic element is directly accessible. The magnetic memory cell can be sensed with a GMR head.

FIELD OF THE INVENTION

The present invention pertains to generally to memory storage devicesand particularly to magnetic memory storage devices.

BACKGROUND OF THE INVENTION

Within the field of memories, there is continuing interest in findingways to increase the storage density and speed of memories. As thepersonal use of small devices gain popularity, the memory of theseequipments has to be modified to match the function and design of thesesmall devices. Particularly, as more and more data needs to be stored inthe memory, the memory needs to have the capacity and speed to handlesuch demand.

The discovery of new phenomena of magnetoresistive (MR) andgiantmagnetoresistive (GMR) effect provided a significant advancement inthe field of memory technology. This phenomena demonstrated thatresistance of multilayer thin film comprised of ferromagnetic layerssandwiching a conducting layer can change significantly depending on thedirection of an external magnetic field.

GMR is observed in magnetic metallic layered structures in which it ispossible to orient the magnetic moments of the ferromagnetic layersrelative to one another. One such type magnetic metallic layeredstructure consists of a stack of four magnetic thin films: a freemagnetic layer, a nonmagnetic conducting layer, a magnetic pinned layerand an exchange layer. Magnetic orientation of the pinned layer is fixedand held in place by the exchange layer. By applying an externalmagnetic field, the magnetic orientation of the free layer may bechanged with respect to the magnetic orientation of the pinned layer.The change in the magnetic orientation generates a significant change inthe resistance of the metallic layered structures. The resistance of thestructure determines the logical value to be stored therein. that arebased on GMR technology, use it to control a sensor that responds tovery small rotations of magnetic orientation of the GMR free layer dueto magnetization on the disk. However, the present use of thistechnology in disk drives require the disk to rotate and head toposition on the track to be read, which requires more than 10 ms. Thedisk drive therefore is not utilizing the full potential of fastresponse time of the GMR which could translate into small access time.The access time using GMR in existing technology generally spans between3 ns-5 ns.

There is a clear need in the industry to develop fast memories which canbe used in disk drives as well as small equipments.

SUMMARY OF THE INVENTION

We have developed a memory cell utilizing the GMR technology which isnot limited to disk drive technology but it may be used in otherequipments such as cell phones, medical devices, high end servers,personal digital assistance (PDA) etc. Our unique memory cell designachieves technical advantages over what is currently available in theindustry.

In one aspect of the invention disclosed herein includes a memory cellwhich comprises of at least two conductive lines to carry current. Amagnetic element is disposed between the conductive lines. A magneticfield is induced by applying a current through the individual conductivelines. The polarity of the current through the conductive lines opposeeach other so that the magnetic field generated by the currents areadditive and provides a resultant magnitude which is the sum of theindependent magnetic field generated by the individual conductive lines.

In another aspect of the invention disclosed herein includes a memorycell which comprises of at least two conductive lines and a magneticelement disposed between the two conductive lines. The conductive linesare shaped such that the conductive lines are disposed outwardly aroundthe magnetic storage element thus exposing the magnetic storage elementso that the magnetic element may be positioned in close proximity withany device that may be used to store or retrieve data.

In another aspect of the invention disclosed herein includes a memorycell which comprises of at least two conductive lines and a magneticelement disposed between the two conductive lines. In this embodimentthe conductive lines and the magnetic element are separated by adielectric. The conductive lines are shaped such that the conductivelines, those carrying the current, are disposed outwardly around themagnetic storage element. Here a third conductive line placed under themagnetic element to provide additional current that may be used toincrease the magnetic field strength.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the invention will be appreciated inconjunction with the accompanying drawings, and a detailed descriptionwhich follows.

FIG. 1 shows a top view of magnetic storage cell 100.

FIG. 1 a shows the side view of the magnetic storage cell shown in FIG.1.

FIG. 2 shows the top view of a magnetic storage cell 200 showing themagnetic storage element 202 exposed.

FIG. 3 illustrates by way of example how the unique design of FIG. 2provides a read head direct access to the magnetic storage element.

FIG. 4 shows the top view of a magnetic storage cell 400 with a readhead 416 placed on top of a dielectric 414.

FIG. 4 a shows a side vies of magnetic storage cell 400 shown in FIG. 4.

FIG. 5 shows the top view of an array of magnetic storage cells 510embedded in a structure 500.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a top view of a magnetic storage cell 100. The magneticstorage cell 100 comprises of at least two conductive lines 102 and 104to carry current and a magnetic element 106 disposed between theconductive lines. When the conductive lines are attached to a currentsupply, (not shown) current will flow through the conductive lines asindicated by arrows 108 and 110. The direction of the current flow isadjusted so that the magnetic field induced by the current through theconductive lines will be cumulative to produce a stronger magneticfield. Data may be accessed by changing the resistance of a read head(not shown) using the GMR technology. In this case the current isflowing in the opposite direction so that the induced magnetic field isin the direction shown by the arrows 112 and 114. The induced magneticfield is used to change the resistance of the read head. The change ofresistance is utilized to read and write data from/into the magneticstorage cell. The conductive lines 102 and 104 are parallel to oneanother and this in turn allows the total current needed formagnetization to be divided among the two conductive lines 102 and 104.

This design provides several advantages over the present designavailable in other magnetic storage devices. First, there are at leasttwo conductive lines to carry the desired current so that the totalamount current may be divided among the conductive lines. As such, byincreasing the amount of current through individual conductive lines 102and 104 by a small amount will increase the net amount of currentavailable for magnetization. Also, by dividing the total current neededamong the individual lines helps to avoid other problems, such asoverheating, generally associated with large amount of current beingcarried by a single line. Generally current in the range of 15 mA to 25mA is needed to induce the desired magnetic field in the range of 60 to100 Gauss. This high amount of current may lead to heating. Thusdividing the current among several conducting lines will prevent suchproblems. Even though here we are showing only two conductive lines tocarry the current, it is understood that more than two conductive linesmay be used to divide the desired current as needed.

Here we have an elliptical shaped magnetic element 106 becauseelliptical shape is not uniform i.e. has shape anisotropy. The advantageof having a shape anisotropy for the magnetic element 106 is that themagnetic field needed to disturb the direction of the magnetic momentsunintentionally is considerably higher compared to isotropic shapes.

FIG. 1 a is a side view of the magnetic storage cell 100 as shown inFIG. 1. This figure shows the direction of the current throughconductive line 102 indicated by arrow 108. This figure also shows thedirection of the magnetic field, induced by the current through theconductive line 102 indicated by arrow 112.

FIG. 2 shows a top view of a magnetic storage cell 200. The magneticstorage cell 200 is made up of at least two conductive lines 202 and 204to carry current and a magnetic element 206 disposed between theconductive lines. When the conductive lines 202 and 204 are attached toa current supply, (not shown) current will flow through the conductivelines. The current through the conductive lines will induce a magneticfield. The unique design in this Figure is such that the conductivelines 202 and 204 take a different shape around the magnetic element 206so that the magnetic element is exposed. Here the conductive linesdisposed outwardly around the magnetic storage element 206 forming anelliptical shape 208 and 210. Even though here the conductive linesaround the magnetic element take on an elliptical shape they can take onother shapes as well such as rectangle, square, circle etc. The onlynecessary component is that the magnetic element 206 be directlyaccessible. The direct access to the magnetic element allows the data tobe stored or retrieved from the magnetic storage cell 216. The directionof the current is indicated by the arrows 212 and 214. Even though herethe direction of the current shown by the arrows 212 and 214 point inthe same direction the polarity of the current can be adjusted in orderto increase or decrease the magnetic field strength. For example, inorder to get a stronger magnetic field the polarity of the currentthrough the conductive lines 202 and 204 may be directed to oppose eachother. With reference to FIG. 2, the direct accessibility provided bythis design in turn will drastically reduce the time needed to retrieveor store the data into the magnetic storage cell. Once again we can readand write data from or to the magnetic storage cell by changing theresistance of the read head (not shown) which depends on themagnetization of the magnetic element located directly underneath it.

FIG. 3 shows an application of a magnetic storage cell 300 of the kinddescribed in FIG. 2. This figure is a cross section of a side view of amagnetic storage cell of the kind shown in FIG. 2. This figure furtherincludes a read head 306 placed above the elliptical shape (not shown)formed by the conductive line 304. This figure further illustrates theuniqueness of this design where the conductive lines are disposedoutwardly around the magnetic storage element 308. Once again the readhead 306 has direct access to the magnetic element 308. Any standardlogic circuit known in the industry can be used to store or retrieveinformation in/from the magnetic storage cell. Accordingly, in thiscase, when the read head receives an instruction to retrieve the datafrom the magnetic storage cell 300, the read head can immediatelyretrieve the data from the storage cell, which is located directlyunderneath the read head 306. Once again this allows faster storage andretrieval of information from the memory.

FIG. 4 is a top view magnetic storage cell 400. The magnetic storagecell 400 shown includes two conductive lines 402 and 404 and a magneticelement (not shown) disposed between the conductive lines 402 and 404.The conductive lines 402 and 404 are disposed outwardly in such a mannerthat they encapsulate the magnetic element. Here the conductive linestake a rectangular shape 409 around the magnetic element. This onceagain provide direct access to the memory cell. By giving a rectangularshape 409 around the magnetic element further provides an increasedinductance which translates into stronger magnetic field to be used.Also, larger surface area helps to reduce the heat dissipation and thusavoiding the use cooling mechanisms.

A read head 416 as shown here may be used to store or retrieve the datainto/from the cell. A dielectric 414 is placed between the read head 416and the conductive lines 402 and 404 to prevent short circuiting. Thismagnetic storage cell 400 further includes another conductive line 422(not shown) below the magnetic element 418. The magnetic element isseparated from the conductive line 422 (not shown) by another dielectricelement 420 (not shown). The conductive line 422 provides additionalcurrent to induce even stronger magnetic field.

FIG. 4 a is a cross section of the type of magnetic storage cell 400shown in FIG. 4. The basic configuration of the magnetic storage celldescribed above includes two conductive lines 402 and 404 and a magneticelement 415 is disposed between the conductive lines. The currentthrough the conductive lines would induce a magnetic field. The magneticelement 415 acts as magnetic field generating means. The resistance ofthe read head 416 depends on the direction of the magnetic fieldgenerated by the magnetic element. Based on the resistance value of theread head a 0 or 1 is stored in the magnetic storage cell.

FIG. 5 shows top view a structure 500 embedded in it is an array ofmagnetic storage cells 510 of the kind described in FIG. 4. The array ofmagnetic storage cell is embedded in a support element 508. The supportelement may be made of semiconductor, ceramic, glass, etc. The storagecell 510 includes two conductive lines 502 and 504. A magnetic element506 is disposed in between the two conductive lines 502 and 504. Each ofthe magnetic element 506 is ensured to contain at least one magneticdomain. A current through conductive lines 502 and 504 would induce amagnetic field. The magnetic element 506 acts as a magnetic fieldgenerating means. Any standard access logic circuits may be used toaccess the storage cell. The access logic decides which storage cell 510should be accessed from the array. Since the conductive lines aredisposed outwardly a read head (not shown) can have direct access to thedata stored in the cell. The direct access helps to prevent the readhead from accessing the wrong magnetic storage cell 510.

The above described preferred embodiments are not intended to limit thescope of the present invention, as one skilled in the art can, in viewof the present disclosure, expand such embodiments to correspond withthe subject matter of the invention claimed below.

1. A magnetic storage cell, comprising: a magnetic element having ashape anisotropy wherein its cross-sectional area along at least oneaxial direction changes along that direction; at least two conductivelines disposed so as to encapsulate the magnetic element; a read head toretrieve data from the magnetic element; and a dielectric layer disposedbetween the read head and the at least two conductive lines.
 2. Themagnetic storage cell of claim 1, wherein the magnetic element has anelliptical cross-section.
 3. The magnetic storage cell of claim 1,wherein the magnetic element has a rectangular cross-section.
 4. Themagnetic storage cell of claim 2, wherein the conductive lines carrycurrent in opposite directions.
 5. The magnetic storage cell of claim 1,wherein the conductive lines when proximate to the magnetic elementfollow a contour of the magnetic element.
 6. A method, comprising: in amagnetic storage cell, using a magnetic element having a shapeanisotropy wherein a cross-sectional area of the magnetic elementchanges along at least one axial direction, the shape anisotropy toreduce a magnetic field required to disturb a direction of a magneticmoment of the magnetic element; encapsulating the magnetic element withat least two current carrying conductors; providing a read head toretrieve data from the magnetic element; and providing a dielectriclayer to separate the read head from the at least two current carryingconductors.
 7. The method of claim 6, wherein the magnetic element hasan elliptical cross-section.
 8. The method of claim 7, furthercomprising passing currents through the conductors in oppositedirections.
 9. The method of claim 6, wherein the magnetic element has arectangular cross-section.
 10. The method of claim 6, wherein theencapsulating comprises forming the current carrying conductors tofollow a contour of the magnetic element.